There are many hydraulic control applications where it is desirable to significantly reduce the time taken to move the primary force producing hydraulic piston of the system in one or both directions of its operative travel. The need can become very significant in physical systems having hydraulic cylinder prime movers that are very large, such as in automobile crushing systems. Depending on their particular designs, such systems may utilize very large prime mover cylinders connected to operate the crushing ram with, for example, bore diameters of 10 to 12 inches and piston strokes from 90 to 100 inches. In such systems, it is desirable not only to crush the automobile in a relatively short period of time, but to then rapidly return the crushing ram to its initial position for the start of the next crushing operation.
Regenerative hydraulic circuit principles have been used to reduce the cycle time of prime mover hydraulic cylinders. The general principal involved in a regenerative circuit is that special valving is used to connect the rod end of the prime mover cylinder with its blind or cap end in a manner so as to increase the rate of travel of the piston. For example, if it is desired to increase the piston travel speed in the primary working direction of the piston, from its blind end toward its rod end, the regenerative network would direct hydraulic system oil that would normally flow to the system tank or reservoir, from the piston's rod end, to supplement the pumped oil being supplied to the piston's blind end--causing the piston to advance at an increased rate of speed toward the rod end.
During a regenerative process, in essence, equal pressure is applied to both ends of the hydraulic cylinder, with the effect that the net thrust delivered by the cylinder rod will be the same as if the effective pressure were applied only to the rod cross-sectional area (i.e., thrust=system pressure.times.rod area). The oil redirected by the regenerative circuit from the rod end of the cylinder, fills an equivalent volume on the blind or cap side of the cylinder so that the hydraulic pump driving the cylinder needs to only fill a space equivalent to the volume of the rod. Such regenerative principles are well known to those skilled in the art.
While such known regenerative principles have been employed to advantage in reducing hydraulic cylinder cycle time, they have typically been employed to assist movement of the piston in only one direction and have typically only directly used a portion of the hydraulic fluid available for redirection. Further, the hardware that has been used to implement regenerative control functions has typically been very large, bulky, heavy, expensive and difficult to install. The ability to decrease cylinder movement cycle time is proportional to the volume of hydraulic oil that can be redirected by the regenerative circuit. However, due in part to the heretofore cumbersome implementation techniques of known regenerative control circuits, they have not been able to practically, effectively and efficiently handle regeneration applications for very large cylinders wherein it is desirable, for example, to redirect significant quantities of oil through oil passageways of greater than 1 inch in diameter.
The present invention addresses the above-described deficiencies of regenerative systems of the prior art. The present invention provides a relatively inexpensive, efficient and effective regenerative circuit that can be made with readily available technology and which gives significant cycle reduction time by enabling virtually 100% regenerative cylinder operation in both directions of travel of the cylinder's piston. These and other features of the invention will become apparent upon a more detailed description thereof.